1. Field of the Invention
The present invention relates generally to a metal gate structure and fabrication method thereof, and more specifically, to a metal gate structure and fabrication method thereof using a titanium aluminum nitride metal layer as a barrier layer and a portion of a work function metal layer.
2. Description of the Prior Art
Poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as the metal-oxide-semiconductor (MOS). With the trend towards scaling down the size of semiconductor devices, however, conventional poly-silicon gates face problems such as inferior performance due to boron penetration and unavoidable depletion effect. This increases equivalent thickness of the gate dielectric layer, reduces gate capacitance, and worsens a driving force of the devices. Therefore, work function metals that are suitable for use as the high-K gate dielectric layer are used to replace the conventional poly-silicon gate to be the control electrode.
In a complementary metal-oxide semiconductor (CMOS) device, one of the dual work function metal gates is used in an NMOS device and the other one is used in a PMOS device. It is well known that compatibility and process control for the dual metal gate is more complicated, while thickness and composition controls for materials used in the dual metal gate method are more precise.